This invention relates in general to the field of semiconductor lasers and optical isolators and more particularly to an inline ferromagnetic-composite isolator and method.
Optical isolators are used in optical communications systems and optical networks to eliminate or reduce reflected light waves. The presence of reflected light waves in such systems and networks may result in significant problems, disadvantages and instabilities, especially when reflected light waves reach or reenter a laser source or optical amplifier.
Conventional optical isolators were developed to eliminate or minimize the presence of reflected light waves. Unfortunately, the manufacture and implementation of conventional optical isolators is complicated, unreliable, expensive and fraught with difficulties and disadvantages.
The implementation of conventional optical isolators is often cumbersome and expensive. For example, conventional optical isolators may use non-reciprocal Transverse Electric (xe2x80x9cTExe2x80x9d) like mode converters and non-reciprocal Transverse Magnetic (xe2x80x9cTMxe2x80x9d) like mode converters, reciprocal TE like mode converters and reciprocal TM like mode converters, an absorption element to absorb modes of light of a particular polarization, and a space periodic magnetic field for quasi-phase match between TE and TM like modes. This phase match requirement of conventional optical isolators is particularly difficult and problematic, and imposes severe fabrication tolerances. For example, the fabrication tolerances on such variables as composition, layer thickness, and interaction length are extremely difficult to consistently achieve and replicate. This causes reliability and performance concerns, along with significantly increased overall costs.
The increased use of semiconductor optical elements and devices, such as semiconductor lasers, laser arrays, and optical amplifiers, have resulted in the need to integrate or interface conventional optical isolators with such semiconductor elements and devices. The different fabrication techniques and materials used in each has made such a solution either impossible or impractical. This has provided additional challenges in integrating and interfacing conventional optical isolators with semiconductor elements and devices.
From the foregoing it may be appreciated that a need has arisen for an inline ferromagnetic-composite isolator and method for use in an optical system or network. In accordance with the present invention, an inline ferromagnetic-composite isolator and method are provided that substantially eliminate one or more of the disadvantages and problems outlined above.
According to an aspect of the present invention, an optical isolator, and method for making the same, is provided that includes a waveguide, with a core and a cladding, and a magnetic-composite material. The waveguide core may include a first end, a second end, and a boundary surface, is operable to allow a light wave incident the first end of the core to propagate from the first end of the core to the second end of the core, which defines a positive propagation direction, and is operable to allow a light wave incident the second end of the core to propagate from the second end of the core to the first end of the core, which defines a negative propagation direction. The waveguide cladding is positioned relative the boundary surface of the core and includes a thinned segment of the cladding with a cladding thickness operable to allow an optical field penetration through the thinned segment of the cladding by a light wave that propagates in the positive propagation direction of the core and that propagates in the negative direction of the core. The thinned segment of the cladding having a length that extends relative to a portion of the core. The magnetic-composite material is provided in the presence of a magnetic field, which is preferably a static magnetic field, with at least a component of the magnetic field oriented in a direction perpendicular to the positive propagation direction of the core parallel to the magnetic vector of the optical field, and is positioned relative the thinned segment of the cladding of the waveguide to receive the optical field penetration through the thinned segment of the cladding. The magnetic-composite material having a thickness and an index of refraction to attenuate a light wave that propagates in the portion of the core in the negative propagation direction by an amount greater than the attenuation of a light wave that propagates in the portion of the core in the positive propagation direction.
According to an aspect of the present invention, an optical isolator, and method for making the same, is provided that includes a waveguide with a guide layer, a first clad layer, a second clad layer, and a magnetic-composite material. The waveguide guide layer may include a first end, a second end, a top and a bottom, is operable to allow a light wave incident the first end of the guide layer to propagate from the first end of the guide layer to the second end of the guide layer, which defines a positive propagation direction, and is operable to allow a light wave incident the second end of the guide layer to propagate from the second end of the guide layer to the first end of the guide layer, which defines a negative propagation direction. The first clad layer of the waveguide is provided relative the bottom of the guide layer, and the second clad layer of the waveguide is provided relative the top of the guide layer. The second clad layer includes a thinned segment with a thickness operable to allow an optical field penetration through the thinned segment of the second clad layer by a light wave that propagates in the positive propagation direction of the guide layer and that propagates in the negative direction of the guide layer. The thinned segment of the second clad layer having a length that extends relative to a portion of the guide layer. The magnetic-composite material is provided in the presence of a magnetic field with at least a component of the magnetic field oriented in a direction perpendicular to the positive propagation direction of the guide layer parallel to the magnetic vector of the optical field, and is positioned relative the thinned segment of the second clad layer of the waveguide to receive the optical field penetration through the thinned segment of the second clad layer. The magnetic-composite material having a thickness and an index of refraction to attenuate a light wave that propagates in the portion of the guide layer in the negative propagation direction by an amount greater than the attenuation of a light wave that propagates in the portion of the guide layer in the positive propagation direction.
Related aspects of the optical isolator of the present invention may include providing the thickness of the magnetic-composite material at an optimal thickness defined by such variables as (i) the thickness where maximum attenuation occurs of a light wave of a known frequency that propagates in the portion of the core in the negative propagation direction, (ii) the thickness where minimum attenuation occurs of a light wave of a known frequency that propagates in the portion of the core in the positive propagation direction, and/or (iii) the thickness where the maximum isolation-to-loss ratio occurs, where the isolation is defined as the attenuation of a light wave of a known frequency that propagates in the portion of the core or guide layer in the negative propagation direction, and the loss is defined as the attenuation of a light wave of a known frequency that propagates in the portion of the core or guide layer in the positive propagation direction. Additional related aspects of the optical isolator of the present invention may include providing the thickness of the magnetic-composite material at a thickness defined by such variables as (i) the thickness that results in a larger optical intensity of the optical field of the light wave of a known frequency that propagates in the portion of the core or guide layer in the negative propagation direction to penetrate the thinned segment of the cladding (or second clad layer) to propagate in the magnetic-composite material, than the optical intensity of the optical field of the light wave of a known frequency that propagates in the portion of the core or guide layer in the positive propagation direction to penetrate the thinned segment of the cladding (or second clad layer) to propagate in the magnetic-composite material.
Other aspects of the optical isolator of the present invention may include a maximum isolation-to-loss ratio that is greater than ten, the magnetic-composite material is made of such materials as (i) a polymer and magnetic particles, (ii) a transparent polymer and magnetic particles, (iii) plastic and ferromagnetic particles such as iron or some other metal, (iv) magnetic particles dispersed throughout a polymer, where the magnetic particles are nanometer sized particles. Another aspect of the present invention may include an index of refraction of the polymer that is equal to or greater than the index of refraction of the clad layer of the waveguide.
Still other aspects of the present invention may include the optical isolator provided inline with an optical fiber, the core of the optical isolator is in communication with a core of the optical fiber, and the cladding of the optical isolator is in communication with a cladding of the optical fiber. Another aspect of the present invention may include the optical isolator that has been monolithically integrated with an optical fiber.
Yet another aspect of the present invention may include the optical isolator that defines the length of the thinned segment of the cladding (or second clad layer) as the length to ensure that a light wave that propagates in the portion of the core or guide layer in the negative propagation direction is attenuated by an amount greater than the attenuation of a light wave that propagates in the portion of the core or guide layer in the positive propagation direction.
The various embodiments and implementations of the present invention provide a profusion of potential technical advantages. A technical advantage of the present invention includes the capability to accurately and inexpensively, especially when compared to conventional optical isolators, fabricate and implement an inline ferromagnetic-composite isolator that provides excellent optical isolation properties.
Another technical advantage of the present invention includes the capability to use existing and available manufacturing techniques and processes, including, for example, conventional semiconductor fabrication processes, to fabricate and implement certain embodiments of the invention. This further reduces overall costs to implement and practice the present invention.
Another technical advantage of the present invention includes the capability to reliably and accurately manufacture optical isolators that provide known and pre-determined optical isolation properties. This increases overall reliability and efficiency.
Other technical advantages are readily apparent to one skilled in the art from the following figures, description, and claims.